JPH01151921A - Recovery of desorbed substance at time of desorption of loaded sorbed material - Google Patents

Abstract

PURPOSE: To efficiently recover desorbate regardless of the kind of the desorbate by supplying a desorbate-contg. desorption gas flowing out of a sorption material to a direct heat exchanger, cooling this gas and supercooling the generated liquid desorbate, then circulating this desorbate to the heat exchanger. CONSTITUTION: The desorption gas is sent by a fan 6 to desorption apparatus 1, 1' where the solvent desorbed therein is desorbed. This desorbate-contg. desorption gas is sent to the direct heat exchanger 8 where the gas is brought into contact with the desorbate recovered from a cooling tank 11 and is cooled to a condensation temp. or below and the desorbate is liquefied. The resultant recovered desorbate is sent through a storage tank 10 to the cooling tank 11 where the desorbate is supercooled by the refrigerants of evaporators 4, 2 of a heat pump. The supercooled desorbate is circulated again to the direct heat exchanger 8.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention provides a method for treating the desorbate resulting from the desorption of a loaded sorbent material by heating it before flowing into the sorbent material and after leaving the sorbent material. It relates to a method of recovery using a desorption gas that is cooled by a desorption gas that is guided in circulation.

Conventional techniques In recovering the expelled desorbate from the loaded sorbent material, the desorbate is recovered by condensation. When condensing at that time, the desorption gas itself contained in the desorption chamber is liquefied, and the sorbent is evaporated with water vapor. When a permanent gas is used as the desorption gas, the desorption gas containing the desorption substance is cooled to at least a temperature lower than the condensation temperature of the desorption substance, with the desorption substance occurring in liquid form. In doing so, indirect heat exchangers are used, the inner walls of which are brought to the required condensing temperature with the refrigerant.

- Generally, the desorbate liquefies on the wall being cooled and can fall and be discharged. West German Patent No. 32013
No. 90 describes a method of this type, in which the heat released from the desorbate-containing desorption gas during cooling is transferred to the gas in order to heat the desorption gas. is supplied to the desorption gas before it enters the sorbent material to be desorbed, and is therefore effectively utilized for the desorption, i.e. using a heat pump device with a closed thermal circulation system, The evaporator of the heat pump device is connected as a cooler for the desorption gas containing desorbate and therefore as a condenser for the desorbate, and the liquefaction device of the heat pump device supplies heat to the desorption gas flowing into the sorbent material. Connected as a heat exchanger. With a heat pump arrangement of this type, the externally supplied energy content (measured in terms of the desorption energy to be provided) can be significantly reduced and the process can therefore be carried out particularly economically.

With this type of cooling, difficulties arise in desorbing high-boiling organic substances, which are located near the surface cooled below the condensation temperature, below the cooling limit temperature of the substance in question, and hence fog formation as a result of supersaturation. This means that there will be areas where The fog droplets remain permanently in the desorption gas and are fed back to the sorption material together with the desorption gas, the organic substances evaporating in the heat supply zone and therefore increasing the partial pressure of the substances in the desorption gas. do. As a result, the sorbent material cannot be fully desorbed. This is because desorption occurs only if the partial pressure of the relevant organic substances in the desorption gas is kept very low.

It should also be taken into account that difficulties arise when desorbing easily degradable organic substances (mainly halogenated hydrocarbons). The difficulty in this case is that the desorption temperature must be kept below the decomposition temperature in order to avoid autocatalytic decomposition in the presence of water. Autocatalytic decomposition leads to the generation of hydrohalic acids, which lead to corrosive damage in the desorption gas circulation system. This is particularly the case when limiting the absolute water vapor content through selective sorption devices containing molecular sheep. The hydrohalic acids produced by the decomposition of halogenated hydrocarbons and circulated in the desorption gas act on the charged molecular sheep, reducing its water separation capacity and therefore reducing the amount of water in the desorbate circulation system. The amount of water will gradually decrease. This increases the hydrohalic acid content, which accelerates the corrosive action.

Problem to be Solved by the Invention The present invention therefore aims to improve the recovery of desorbate, while avoiding these difficulties, irrespective of whether it concerns organic substances that tend to boil at high temperatures and form fogs or that have a low boiling point. It is based on the task of proposing the development of a process that can be carried out, whether or not it concerns e.g. halogenated hydrocarbons, which tend to decompose.

Means for Solving the Problem This problem is solved in a surprisingly simple manner by the method described in the claims.

According to the method, a closed desorption gas circulation system is conducted directly via a heat exchanger in which the desorption gas to be cooled to a temperature below the condensation temperature of the desorption mass is cooled to a temperature below the condensation temperature of the desorption mass. is subcooled to a temperature significantly below (taking care of the partial pressure) and in direct contact with the recovered desorbate, thereby cooling the desorbed gas. In this case, the condensate is directly absorbed by the liquid desorbate introduced in the heat exchanger. This corresponds to direct condensation, where good heat transfer is achieved with low temperature differences. This is because there is no heat exchange surface to prevent heat transfer. As a result of the slight temperature difference, flange formation does not occur. Due to the absence of fog, the residual content of desorbate in the desorption gas is low and the partial pressure of the desorbate, even after heating, corresponds to the partial pressure at the condensation temperature. Effective desorption of sorbent materials is therefore possible.

Adsorption of the produced hydrohalic acid is achieved in low boiling substances. In the liquid phase, the recovered desorbate is treated and worked up in such a way that measures to avoid any possible decomposition of the halogenated hydrocarbons can be easily carried out in this liquid phase.

In direct cooling by condensation, absorption is relevant, so it is irrelevant whether the cooler is operated in cocurrent or countercurrent. In the case of the generation of a large amount of heat of condensation and the associated significant heating of the supercooled desorbate introduced, a countercurrent system is advantageous. This is because the residual content of desorbate is essentially determined by the inlet temperature of the supercooled desorbate in the gas exit zone.

This is advantageously carried out using a heat pump device, which transfers the heat generated by the subcooling of the liquid desorbate back to the desorption gas, ie absorbs the heat from the liquid desorbate by means of an evaporator. A refrigerant circuit of the heat pump device transfers this heat to the liquefaction device, which donates heat to the desorption gas. It is clear that cascaded devices are also useful, especially if wider temperature differences are to be generated. Furthermore, it is clear that the desorption temperature can be obtained by additional post-heating if this is not guaranteed by a direct heat pump device. However, taking into account the heat requirements, this subsequent heating can be adjusted to be smaller than the amount of heat delivered by the heat pump device.

To achieve good subcooling of the liquid desorbate to be fed directly to the heat exchanger, the cooling of the liquid desorbate is carried out in the tubes connected to the direct feed of the desorbate to the heat exchanger. It is advantageous to do so. For this purpose, this tube is configured as a heat exchanger,
For example, attaching a flexible pipe or sleeve that constitutes an evaporator,
In this case, the peripheral wall is designed as an evaporator.

In this device, the unavoidable heat losses of the pump promoting the liquid desorbate are also released.

If consideration is given to the generation of large amounts of heat of condensation, it is advantageous to collect the desorbate in a tank and to cool it in this tank, for which purpose the evaporator of the heat pump arrangement is installed in this tank. In this way, as much heat as possible extracted from the desorption material is utilized. It is also clear that both devices can be combined with each other.

The process is particularly advantageous for suppressing the decomposition of halogenated hydrocarbons if an acid binder (stabilizer or acid acceptor) is added to the recovered desorbate which is directly charged into a heat exchanger. This type of stabilizer or acid acceptor is described in West V.I. Patent Publication No. 1084.
It is known from US Pat. No. 713. At least one organic hydrazine compound, alcohol, epoxide and phenol
A mixture of species is applicable. These suppress the autocatalytic decomposition of the halogenated hydrocarbons and achieve the binding of any liberated hydrohalic acids in the liquid phase. Therefore, these acids have no effect and therefore the evaporation of the hydrohalic acids is also prevented while the liquid desorbate in the desorption gas remains in the cooler. Since the moisture content is a determining factor for the decomposition of halogenated hydrocarbons, it is advantageous to monitor the moisture content of the desorption gas and meter the acid binder accordingly. Monitoring the moisture content of the desorbed gas is equivalent to monitoring the moisture content of the desorbed material that is collected and cooled. It is advantageous to use a pump provided to introduce the recovered desorbate directly into the heat exchanger for the addition of the acid binder, and in this case, the negative pressure on the suction side is used as the suction pressure for the acid binder. In addition, a metering valve is provided in the inlet to the suction side of the pump for metering.

A particularly effective way to limit the decomposition of halogenated hydrocarbons is to connect an adsorption device for selective water separation, which acts as a dryer, between the cooler and the heater in the desorption gas circuit. Generally, adsorption devices of this type are loaded with molecular sheep, silicate glue, or similar dry materials.

In order not to impose unnecessary loads on this adsorption device, the desorption gas circulation is divided into two sub-streams, only one of which flows through the adsorption device, and the other sub-stream is guided around the adsorption device. By adjusting one of the gas streams, the adsorption device flow rate can be adjusted to a desired value between approximately 0 and 100%. Since the water is first driven out in each case during desorption, the operating time during which the adsorption device is activated is the initial stage of desorption. Switching is therefore possible so that the adsorption device is not loaded with organic substances, which are subsequently pumped out. By adjusting one partial stream, which results in a corresponding adjustment of the second partial stream, the partial gas stream flowing through the adsorption device functioning as a dryer can always be adapted to the operating conditions according to the invention, This is the case, for example, if the water content of the desorbed gas is monitored and this is recognized as an adjustment variable for the throttle valve adjustment.

Example One example of this method is described below.

The exhaust air discharged from an industrial process and containing a solvent mixture of methyl chloride and ethanol is purified in a filter. The filter contains activated carbon, the amount of which is 30% in two layers.
The exhaust air, present at 00 kt, carries a quantity of 100 k/h of solvent, which is adsorbed to almost 100% on the activated carbon. After an 8 hour shift, the activated carbon containing about 600-800 ky is nearly saturated and the solvent can be recovered. For this purpose, nitrogen is desorbed in the gas circulation system by 4
Heat to 50K, circulate and pass through activated carbon.

The effluent nitrogen transports an amount of desorption solvent of up to 370 kg/h so that the desorption time lasts 2-3 hours, and 5-6 hours is sufficient to cool the desorbed activated carbon.

The nitrogen containing desorbed solvent is recooled to about 300-320K, which is above the condensation temperature of the solvent. To recool the solvent, the nitrogen is directly quenched in a heat exchanger by sucking the liquid into it. This liquid is a mixture of methyl chloride and ethanol, which is a mixture of solvents initially used in the industrial process and later condensed desorbates. This quenching liquid is subcooled to about 265 K, which is above the condensation temperature of the desorbed solvent (ie, this is what is meant by "subcooled"). This cooling takes place in a heat exchanger, which is the evaporator of a closed circulation heat pump. The heat transferred by the heat pump brings it to a higher temperature level and can be used to heat or preheat the nitrogen before it enters the activated carbon filtration. Amount 3
70 ky/h of liquid desorbate flows out as a production amount.

Sodium hydroxide is added as a corrosion inhibitor to the quench liquid at a concentration of 5 o ppm to suppress corrosion problems caused by hydrochloric acid generated by hydrolysis of some of the methyl chloride.

Next, the gist of the present invention will be explained in detail with reference to method process diagrams shown in FIGS. 1 and 2 of the accompanying drawings, which are examples.

Connected to the gas purification device are two adsorption devices 1 and 1' filled with sorbent material, which devices are connected to a valve 2.
．． 1. 2.2 and 2.1', 2.2' can be selectively separated from the gas stream. In the embodiment shown, the adsorption device 1' is provided for gas purification, and the gas to be purified does not flow through the adsorption device 1 with the valve closed. For desorption, both adsorption devices 1 and 1' are connected to a desorption gas circulation system, with valves 3.1 and 3.1' and the adsorption device connected before the desorption gas inlet into the adsorption device. Valves 3.2 and 3.2' are provided after the desorption gas outlet from. Thereby, the adsorption device 1 which does not take part in the gas, f# production operation is connected to the desorption gas circulation system by means of valves 3.1 and 3.2 which are open as shown. It is advantageous to use nitrogen or an inert gas with a low oxygen content as the desorption gas.

The desorbed gas is conveyed through the circulation system by a blower 6, which is connected to a coupling pipe 7.1. 7.2 and 7.3.

A pipe 7.1 connects the outlet of the blower 6 with the adsorption device 1, which is filled with the desorption material to be desorbed. A pipe 7.2 connects the adsorption device 1 directly to the cooler 8, and a pipe 7.3 connects the cooler 8 to the air blower wR6. tube 7
．． A heater 7.4 of an indirect heat exchanger is connected in 1, in which the heat emitted by the evaporator 4.1 of the heat pump arrangement is transferred to the desorption gas. In order to dry the desorbed gas, a water-selectively operated adsorption device 9 can be connected, which device is connected parallel to the line 7.3, in which = Advantageously, a W valve 9.2 is provided.

This regulating valve 9.2 makes it possible to regulate the desorption gas flow flowing through the adsorption device 9, which operates as a dryer, by approximately 0 to 100%. An adjustment can also be made when installing the adjustment drive, in which case, for example, the moisture content of the desorption gas can be used as a measure for triggering the adjustment. In order to completely separate the adsorption device acting as a dryer from the desorption gas stream, a stop valve can be installed in the adsorption device tube 9.1. Since the desorption device 9 connected as a dryer is also useful as a heat and water storage and absorbs heat and releases moisture during the cooling phase, the temperature of the desorption gas can also be used as another measure. At that time, you should pay attention to the operating condition. This is because the adsorption device 9, which operates as a dryer,
This is because water is adsorbed during the desorption of the adsorbent material in the adsorption device 1, and is desorbed by ejection of water vapor itself during the cooling stage of the adsorption material in the adsorption device 1.

In the direct heat exchanger 8, the desorbate-containing desorbent gas contacts the recovered desorbate from the cooling tank 11.

Subcooling is carried out by means of an evaporator 4.2 of a heat pump device installed in the cooling tank 11, which evaporator is connected at one connection side to the suction side of the pressure generator 5. The pressure side is connected via one of the two pipes 4.3 to a liquefier or condenser 4.1 in a heater 7.4. The other pipe 4.3 returns the refrigerant from the circulation system of the heat pump device, which has been liquefied in the liquefier, back to the evaporator 4.2, and adjusts the recovered and desorbed substances in the cooling tank 11 by adjusting the throttle before its inflow. evaporation and therefore effective cooling is possible. After supercooling, the recovered desorbate is sucked out of the cooling tank 11 by a transport pump via line 11.1 and introduced directly into the heat exchanger 8 via line 11.2.

This introduction takes place via a distribution device 8.2, and the introduced desorbent is directly transferred to the internal structural components or cross-members of the heat exchanger (
Here it flows via the shelf 8.1) and absorbs heat and the desorbed matter that condenses in the process. The heated and condensed desorbate leaves the heat exchanger 8 via the condensed desorbate, which opens into the collecting vessel 10 for the recovered desorbate. and is immersed below the liquid surface to close the desorbate circulation system in the container 10. A constant liquid level is maintained in the storage tank 10 for the collected desorbate by means of an overflow pipe 10.1, through which excess desorbate is discharged from the storage tank into a collection tank. A cooling tank 11 is provided separately for the storage tanks 10 and '.
This tank 11 is connected to the storage tank 10 through a pipe 10.2t.
and has a liquid level directed to it (in closed liquid containers, pressure regulation takes place above the liquid level, as is required especially in the case of low-boiling substances). ). Heat is absorbed from the recovered desorbent flowing in the cooling tank 11 by the refrigerant evaporated in the evaporator 4.2 of the heat pump device, and the desorbent is supercooled, and the recovered desorbent is supercooled.
It reaches again into the tip for direct introduction into the heat exchanger 8.

In front of the suction connection of the pump 12, a tube 13.1 opens into a tube 11.1 which guides the subcooled recovered desorption material. The tube 13.1 connects to a storage container in which the acid binder, stabilizer or acid acceptor is stored ready for use. With this device, you can eliminate the need for additional pump installation.
It is possible to add and mix only the pressure ratio of the acid binder to be added into the subcooled desorbate in the tip to the direct heat exchanger. It is advantageous to configure the mixing point as an injector 11.3, which significantly increases the suction effect and
If necessary, it is also possible to feed in the substances to be added via a certain height difference. Restriction 13 connected into pipe 13.1
．． 2 allows the desired dosing. If the throttle point is designed as a regulating throttle, the metering can be adjusted. A regulating drive is provided to control the regulating throttle as a brightening throttle, which also facilitates the controlled supply of acid binder or other substances to be metered into the supercooled desorbent.

In this case, the control can be correlated, for example, with the moisture content of the desorbed gas or the moisture content of the recovered desorbed material (preferably measured in the return line 8.3).

The alternative according to FIG. 2 shows another arrangement of heat exchangers 4.2 for subcooling the liquid desorbate. A heat pump arrangement consisting of a compressor 5, a liquefier 4.1 and an evaporator 4.2, which are connected to each other via a pipe 4.3, is configured so that the evaporator 4.2 directly feeds the heat exchanger 8. A tube 11 that guides the liquid desorbent to be removed.
．． 2 to form a heat exchanger for transferring heat from tube 11.2 to tube 4.3. In this way, the liquid desorbent guided through the tube 11.2 is supercooled. This arrangement, which is also possible by including the pipe 11.1 from the storage tank 10 to the pump 12, has the advantage that the heat losses transferred to the liquid desorbate in the pump 12 are also collected. Therefore, the method of cooling the liquid desorbate illustrated in FIG. 2 can be carried out when the condensation temperature is very low.

Regarding the cooling of liquid desorption substances, a special cooling tank 11 is not absolutely necessary, the evaporator 4.2 is replaced by the storage tank 10.
It may be installed inside. Evaporator 4.2 of the heat pump device and tube 11.1 or 11 serving as a direct cooler
．． 2 to form a heat exchanger, the cooling tank 11 can be omitted. Finally, it is also conceivable to omit the storage tank 10 so that the discharge tip of the direct heat exchanger 8 forms a buffer space for the desorbed mass through the direct heat exchanger 8.

In this case, the return pipe 1 that supplies liquid desorbent to the pump 12
1.1 directly into the vessel tip of the heat exchanger 8. As shown, perforated shelves can be provided in the direct heat exchanger 8, as well as ring-shaped packings or the like from inserts known in the method technology.

[Brief explanation of the drawing]

FIG. 1 shows a process diagram of the method of the invention, and FIG. 2 shows a process diagram of an alternative method. 1, 1', 9... Adsorption device, 8... Direct heat exchanger, 10... Storage tank, 11... Cooling tank,
13...Storage container Figure 1 13. Storage container diagram 2

Claims (1)

[Claims] 1. The desorbate produced during the desorption of the loaded sorbent material by a desorbent gas that is heated before entering the sorbent material and cooled after leaving the sorbent material. In the method of recovering, the desorbing gas containing the desorbing material flowing out from the sorbing material is fed to a direct heat exchanger functioning as a cooler, in which the desorbing gas is cooled by the recovered desorbing material to a temperature lower than the condensation temperature, Desorbing the loaded sorbent material, characterized in that the recovered desorption material in liquid form is introduced into the cooler and the liquid desorption material is supercooled before entering the cooler. A method for collecting the desorbed matter produced during the process. 2. The method according to claim 1, wherein the desorption gas is guided in parallel flow with the recovered desorption substance to be introduced to be supercooled. 3. The method according to claim 1, wherein the desorbed gas is guided through the cooler in countercurrent to the recovered desorbed material to be supercooled. 4. The heat extracted from the liquid desorbate before it flows into the cooler is extracted using the evaporator of the heat pump device, and the heat is supplied to the liquefaction device using the refrigerant circulation system, and the heat is extracted in the liquefaction device. Claim 1 wherein heat is transferred to the desorption gas guided by the sorption material.
The method described in any one of (3) to (3) above. 5. The method according to any one of claims 1 to 4, wherein the liquid desorbate supplied to the direct heat exchanger is cooled in a tube connected directly to the heat exchanger. 6. The method as claimed in claim 1, wherein the liquid desorbate fed directly to the heat exchanger is intermediately stored in a storage tank and cooled in the storage tank. 7. The method according to claim 1, wherein an acid binder, a stabilizer and/or an acid acceptor are added to the supercooled recovered desorbate to be introduced. 8. The method according to claim 7, wherein the added acid binder, stabilizer or acid acceptor is aspirated by a mixing injector. 9. The method according to claim 7 or 8, wherein the acid content of the desorbate and/or the desorbent gas is monitored and the dosage of the acid binder, stabilizer or acid acceptor is controlled by the acid content. 10. The method according to claims 1 to 9, wherein the desorption gas flowing out of the direct heat exchanger functioning as a cooler is divided into two sub-streams, with the water being removed from one of the sub-streams in an adsorption device functioning as a dryer. The method described in any one of the above. 11. The method according to claim 10, wherein one of these divided flows is adjustable by a throttle valve. 12. Claim 11, wherein the magnitude of the divided flow flowing through the adsorption device functioning as a dryer is controlled by a regulating drive of a throttle valve.
Method described.